1. Field of the Invention
The present invention relates to an electroluminescence display device, and more particularly, to an organic electroluminescence display device and a method of fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for fabricating a reliable electroluminescence display device.
2. Discussion of the Related Art
A cathode ray tube has been widely used as a display device such as a television and a computer monitor. However, the cathode ray tube has large size, heavy weight, and high driving voltage. Therefore, flat panel displays having characteristics of being thin, light weight, and low in power consumption have been in demand. The flat panel displays include a liquid crystal display device, a plasma display panel device, a field emission display device, and an electroluminescence display device.
The electroluminescence display device may be categorized into an inorganic electroluminescence display device and an organic electroluminescence display device depending upon a source material for exciting carriers. The organic electroluminescence display device has drawn a considerable attention due to its high brightness, low driving voltage, and natural color images from the entire visible light range. Additionally, the organic electroluminescence display device has a great contrast ratio because of self-luminescence. The organic electroluminescence display device can easily display moving images due to its short response time of several microseconds, and is not limited by a viewing angle. The organic electroluminescence display device is stable at a low temperature, and its driving circuit can be easily fabricated because it is driven by a low voltage. Besides, a manufacturing process of the organic electroluminescence display device is relatively simple.
In general, an organic electroluminescence display device emits light by injecting electrons from a cathode electrode and holes from an anode electrode into an emissive layer, combining the electrons with the holes, generating an exciton, and transiting the exciton from an excited state to a ground state.
Since its luminous mechanism is similar to a light emitting diode, the organic electroluminescence display device may be called an organic light emitting diode (OLED).
FIG. 1 shows a band diagram of a related art organic electroluminescence display. As shown in FIG. 1, the related art organic electroluminescence display includes an anode electrode 1, a cathode electrode 7, a hole transporting layer 3, an emissive layer 4, and an electron transporting layer 5 disposed between the anode electrode 1 and the cathode electrode 7. The related art organic electroluminescence display device further includes a hole injection layer 2, which is disposed between the anode electrode 1 and the hole transporting layer 3, and an electron injection layer 6, which is disposed between the cathode electrode 7 and the electron transporting layer 5, to efficiently inject holes and electrons.
The holes and the electrons are injected into the emissive layer 4 through the hole injection layer 2 and the hole transporting layer 3 from the anode electrode and through the electron injection layer 7 and the electron transporting layer 5 from the cathode electrode 7, respectively, thereby generating an exciton 8 in the emissive layer 4. Then, light corresponding to energy between the hole and the electron is emitted from the exciton 8.
The anode electrode 1 is formed of a transparent conductive material having a relatively high work function such as indium-tin-oxide and indium-zinc-oxide, and the light is observed at the anode electrode 1. On the other hand, the cathode electrode 7 is formed of an opaque conductive material having a relatively low work function, such as aluminum, calcium, and aluminum alloy.
FIG. 2 is a schematic plane view of the organic electroluminescence display device in the related art. As shown in FIG. 2, the organic electroluminescence display device includes a transparent substrate 10 and a canister 50. A sealant 70 is formed between the substrate 10 and the canister 50, and defines an array region “A”.
FIG. 3 is a cross-sectional view of the related art organic electroluminescence display device taken along line III—III of FIG. 2. As shown in FIG. 3, a plurality of anode electrodes 21 are formed in the array region “A” on the transparent substrate 10, and an organic emissive layer 30 is formed on the plurality of anode electrodes 21. A cathode electrode 40 is formed on the organic emissive layer 30 and extends to one end of the transparent substrate 10. The canister 50 is spaced apart and arranged over the transparent substrate 10. The sealant 70 is disposed between the canister 50 and the transparent substrate 10, and forms an airtight space 80 to protect the organic emissive layer 30 from external moisture and air. The airtight space 80 is filled with an inert gas. Meanwhile, a desiccant 60 is formed on the inner surface of the canister 50. Here, a part of the sealant 70 may be disposed between the canister 50 and the extended portion of the cathode electrode 40.
However, moisture or air is permeated through the airtight space 80 through the gap between the sealant 70 and the canister 50 or between the sealant 70 and the transparent substrate 10. Therefore, it causes malfunction of the organic electroluminescence display device, and a lifetime of the organic electroluminescence display device is reduced significantly.
Additionally, since the sealant 70 should become much larger in size as the size of the device gets larger, it is more likely that moisture or air is permeated through the airtight space 80. Thus, a lifetime of the organic electroluminescence display device is shortened.